Allright, the pics :
I'm just waiting for new knobs.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I'm just waiting for new knobs.
Nice retro ones.
(although my preference goes to symmetrical knobs, and 3 knobs is a bit of a crowd)
You are leaving the Front 'Liège' as is, Ben ?
(although my preference goes to symmetrical knobs, and 3 knobs is a bit of a crowd)
You are leaving the Front 'Liège' as is, Ben ?
The knobs couldn't be more retro, they come from an old 2W tube amp which was beyond repair. No tone controls but : volume, balance, source selection (cd, tuner, phono). The basics 😉 I'll get wooden knobs and put some varnish on everything I think.
I did read through most of these discussions of this wonderful
"Symasym amp" and just wanted to know is the current version
of this amp is a good match for my ATC SCM20SL?
"Symasym amp" and just wanted to know is the current version
of this amp is a good match for my ATC SCM20SL?
Hi Mikewong,
Only you can answer that in the end. I think the Symasym is worth building. What you get out will depend on using good parts.
-Chris
Only you can answer that in the end. I think the Symasym is worth building. What you get out will depend on using good parts.
-Chris
Chris,
do not overemphasize "good parts". What I can see here is a plenty of mistakes in construction, shielding and wiring. And you guys even appreciate these photos. No miracle parts will save these faults.
do not overemphasize "good parts". What I can see here is a plenty of mistakes in construction, shielding and wiring. And you guys even appreciate these photos. No miracle parts will save these faults.
pma is speaking truth. 
many of us have comments often on things like watching distortion readings change when simply doing things like moving wires around or changing the location for a ground connection. this kind of thing can easily keep a great design from getting anywhere near to its potential!
mlloyd1
many of us have comments often on things like watching distortion readings change when simply doing things like moving wires around or changing the location for a ground connection. this kind of thing can easily keep a great design from getting anywhere near to its potential!
mlloyd1
PMA said:
mlloyd1 and PMA , this is a very interesting point you raise. Would you be able to give us an example or two to illustrate how this might be so in the symasym ?
Hi Pavel,
As I like to say, when is a ground not a ground? I still see issues with the PCB design in this regard.
Anyway, and I think you will agree Pavel, the point is that you will only get out of this amp what you put into it's construction. This comment should then encompass all your concerns.
As for the photos of my amps, they are simply on a test jig. No attempt was made to do everything correctly. They were simply connected to check the amplifiers operation and get a rough idea of the sound. BTW, speaker returns went to a separate ground terminal.
-Chris
I did not intend to recommend "boutique parts" at all. I was assuming the wiring would be up to snuff and properly done. Especially grounding where most errors are made. I was merely trying to say that you can not expect the performance this amp is capable of if you use ceramic caps and bulk carbon composition resistors. I personally do not believe in "magic" parts. Just look at my entire history of posts for confirmation of this.
As I like to say, when is a ground not a ground? I still see issues with the PCB design in this regard.
Anyway, and I think you will agree Pavel, the point is that you will only get out of this amp what you put into it's construction. This comment should then encompass all your concerns.
As for the photos of my amps, they are simply on a test jig. No attempt was made to do everything correctly. They were simply connected to check the amplifiers operation and get a rough idea of the sound. BTW, speaker returns went to a separate ground terminal.
-Chris
i have not built any sysmasym (yet), so i cannot make specific comments on it.
i have seen this effect on any number of reasonable to very high performance prototype circuits; analog, digital doesn't matter. i can imagine this is one reason why some manufacturers don't cry a lot about giving away schematics - they know it is not trivial to go from schematic to an actual product that meets/exceeds the desired performance criteria. it can be real trying work to resolve issues in construction, layout, lead dress, grounding, rail bypassing, etc. there is no question these things can make or break a design.
mlloyd1
i have seen this effect on any number of reasonable to very high performance prototype circuits; analog, digital doesn't matter. i can imagine this is one reason why some manufacturers don't cry a lot about giving away schematics - they know it is not trivial to go from schematic to an actual product that meets/exceeds the desired performance criteria. it can be real trying work to resolve issues in construction, layout, lead dress, grounding, rail bypassing, etc. there is no question these things can make or break a design.
mlloyd1
anatech said:
Everywhere ?
I know that the PCB has issues regarding ground / voltage rails, visible as even harmonics in measurings.
I think, when Chris told to use "good parts", he meant not to use "bad parts", like most ceramic caps and carbon resistors.
Mikewong, about your question, i only can say that i got no complaints yet that symasym would not have been able to drive a specific speaker. I know of at least one using symasym with electrostats... (Hi John !)
As symasym itself is uncolorized, there should be no matching issue.
Mike
Hi mlloyd1,
Thanks, but this is in all minds. It is why we do what we do. I can't imagine not trying to do a good job on something.
Hi Mike,
Yes. (you got my meaning). Also I think that Pavel and yourself have done a very good job with this compact PCB. Nothing is ever perfect in this world. I am thinking of ways to separate the "dirty" ground from the "reference" ground.
-Chris
Thanks, but this is in all minds. It is why we do what we do. I can't imagine not trying to do a good job on something.
Hi Mike,
Yes. (you got my meaning). Also I think that Pavel and yourself have done a very good job with this compact PCB. Nothing is ever perfect in this world. I am thinking of ways to separate the "dirty" ground from the "reference" ground.
-Chris
Jfets in symasym... So, i finally tried it, replaced mpsa18 with 2sk170...
Jfets...
This change was definitely an improvement... The sound got more relaxed/softer, at the same time more detailed, deep bass increased.
The difference is subtile, but clear enough to detect without AB-comparison.
To any who have voltage supply at 36 volts or lower and access to sk170, really worth a try ! (i matched them to ~1%)
DC-offset dropped from 3 mv to 2mv...
Maybe jfets are THE devices for input diffamp ?
Mike
Jfets...
This change was definitely an improvement... The sound got more relaxed/softer, at the same time more detailed, deep bass increased.
The difference is subtile, but clear enough to detect without AB-comparison.
To any who have voltage supply at 36 volts or lower and access to sk170, really worth a try ! (i matched them to ~1%)
DC-offset dropped from 3 mv to 2mv...
Maybe jfets are THE devices for input diffamp ?
Mike
JFets & Symasym
Hei Mike
Just for the sake of curiosity how do you replace the MPSA18 by
k170 on a mirrored PCB?
This is a good one for you...and for me,, if I wanted to do that!
I really would like to try it but again I don't think my mirrored amp
(PCB) would take those without a lot of thinking.....
Hei Mike
Just for the sake of curiosity how do you replace the MPSA18 by
k170 on a mirrored PCB?
This is a good one for you...and for me,, if I wanted to do that!
I really would like to try it but again I don't think my mirrored amp
(PCB) would take those without a lot of thinking.....
Hi John, no problem, simply put the sk170 mirrored to the mpsa18 to the pcb. The sk170 has the gate in its middle. You can't do anything really wrong, in theory Drain & Source are interchangable for jfets... (One of the unique features of jfets)
Replacing the mpsa18 with sk170 is a simple drop in.
Mike
Replacing the mpsa18 with sk170 is a simple drop in.
Mike
actually, i beleive the drain and source are interchangable without difference primarily for lower gain devices. i'm not sure the 2SK170 is such a device, but it won't be damaged and will likely still work ok.
mlloyd1
mlloyd1
MikeB said:Jfets in symasym... So, i finally tried it, replaced mpsa18 with 2sk170...
Jfets...
This change was definitely an improvement... The sound got more relaxed/softer, at the same time more detailed, deep bass increased.
The difference is subtile, but clear enough to detect without AB-comparison.
To any who have voltage supply at 36 volts or lower and access to sk170, really worth a try ! (i matched them to ~1%)
DC-offset dropped from 3 mv to 2mv...
Maybe jfets are THE devices for input diffamp ?
Mike
WRT jfet vs bjt for dif pair have you tried degenerating the bjt to the
same transconductance as the jfet ie; about 15 to 20 ohms in each emitter?
As such the bjt will be -much- more linear.
Balanced source impedance is also more important with bjt but
in case of Symasym difficult to achieve.
cheers
Terry